1. Field of the Invention
This invention relates to lead-acid batteries having gelled electrolytes and methods for making such batteries.
2. Description of the Prior Art
Gelled electrolyte lead-acid batteries are known and have been available for commercial use since the early 1920's, as evidenced by the May 15, 1921 issue of The Commercial Car Journal, page 102.
Of the patent prior art, U.S. Pat. Nos. 1,389,750; 1,416,195; 1,417,007; 1,572,586; 2,483,868; 3,305,396; 3,257,237; 3,457,112 and 3,711,332 are known to applicant. Of these, U.S. Pat. Nos. 3,711,332 is most relevant to the apparatus aspect of this invention while U.S. Pat. Nos. 2,483,868 and 3,305,396 are most relevant to the method aspect of this invention.
Concerning the apparatus aspect of the invention, U.S. Pat. No. 3,711,332 discloses utilizing a ratio of sulfuric acid to aqueous sodium silicate solution (Na.sub.2 SiO.sub.3) of from 6:1 to 10:1 to form the electrolyte gel, with the ratio of sodium silicate to water forming the aqueous sodium silicate solution being about 1:1. Sodium silicate, Na.sub.2 SiO.sub.3, as disclosed and taught by U.S. Pat. No. 3,711,332, is conventionally referred to as "water glass."
U.S. Pat. No. 3,711,332 uses electrolyte which forms a liquid phase above the gel phase in the battery, with the two phase system (consisting of the liquid and the gel) changing proportions during battery operation. The liquid phase enters the gel phase during battery discharge and reemerges from the gel phase during battery charging. Depending upon the assumption used for the specific gravity of the sodium silicate and the resultant sodium silicate solution, the ratio of sodium silicate to sulfuric acid ranges from 5.5 to 9.1 in U.S. Pat. No. 3,711,332 (for sodium silicate specific gravity of 2.4), ranges from 14.6 to 19.4 in U.S. Pat. No. 3,711,332 (for sodium silicate specific gravity of 1.4) and ranges from 10.9 to 18.2 in U.S. Pat. No. 3,711,332 (for sodium silicate specific gravity of 1.2).
U.S. Pat. No. 2,483,868 discloses production of 94% anhydrous silica gel at column 1, line 4. Silica, as sodium silicate solution, is sprayed into sulfuric acid to form a sol which turns to a gel as taught at column 2, line 7 of '868. As high as 17% silica results. The sulfuric acid is maintained in a baffled tank.
U.S. Pat. No. 3,305,396 recites that it is known to produce colloidally dispersed silicon as silicic acid for use in dry electrolytes, having a silica particle size of five (5) to twenty (20) microns or less, as taught at column 1, lines 26 and 31. '396 relates to dry cells with electrolytes consisting of sulfuric acid with colloidal silicic acid, as taught at column 1, line 60. The thixotropic electrolyte consisting of sulfuric acid and colloidally dispersed silicic acid is reduced to liquid in a high speed mixer and introduced into the cell housing in an evacuated space, as taught at column 1, line 69. The silicic acid is produced by the pyrogenic method from silicon tetrachloride and is free from alkaline substances, as taught at column 3, line 5.
Prior art practice includes using solid fumed silica (SiO.sub.2) and combining that with H.sub.2 SO.sub.4 in a mixing process which takes about 12 hours and pouring the resultant slurry into a dry charged battery. This process is exceedingly time consuming and expensive.
Aqueous dispersions of colloidal alkali metal silicas are known for use as binders in ceramic investment shell casting and foundries with alcohol being combined with the aqueous colloidal dispersion when faster shell drying and earlier green strength is desired. Using an aqueous colloidal dispersion of an alkali metal polysilica, specifically sodium polysilica, results in ceramic investment shell castings having very smooth surfaces and very close design tolerances.
In the past, some artisans have mixed dry fumed silica with sulfuric acid to provide a gel for introduction into a lead-acid battery precursor. This mixing procedure is quite time consuming, typically taking from 18 to 24 hours for mixing. The dry fumed silica is very fine, making it very difficult to handle. The dry fumed silica-sulfuric acid blend is difficult to keep sufficiently liquid so that the blend flows easily enough to be introduced into the battery precursor. In this prior practice, the fumed silica blend material is converted into the gel form before being introduced into the battery; the thixotropic characteristic of the gel blend material makes it feasible to hold the gel in a liquid condition through continuous mixing and to introduce it into the battery, but with some difficulty.